This invention relates to electrical power supplies, and more particularly to an electrical power supply that accommodates a wide range of input voltages.
It is conventional industrial practice to provide multiple input voltages by dedicated multiple primary windings or series/parallel configurations of a transformer. This is exemplified in the article "How To Specify Power Transformer and Filter Ratings" on pages 20 and 21 of Transformer Catalog F-1, published by Signal Transformer Company on 16 Jan. 1989. These are expensive constructions and can only address one or two input voltage ranges.
It is also conventional practice to provide multiple input voltages by voltage reduction by input impedence. A resistor or capacitor is used as a series impedence to drop the input voltage to a usable level. This utilizes low efficiency high power dropping resistances to dissipate the excess power. It affords a limited input voltage range and incurs high power dissipation. This is exemplified by Motorola O-Voltage Controller UAA 106B disclosed by Motorola Semi-Conductor Technical Data in DL128 REV.3 First Quarter 1990, pages 4-134 and 4-135.
In another practice, disclosed in U.S. Patent No. 4,389,702 switching power supplies reduce the input voltage by an expensive combination of a transformer and active switching circuitry.
Efforts have been made to provide a power supply with electronic circuitry by which a range of input voltages is processed to produce a predetermined output voltage. This type of power supply is described in "Power Supplies Go Solid State" by Robert Burnett and Charles A. Little, Design News 65-89, pages 179; 180; 181; and 182. The cost of manufacture is quite high and the structures afford only a limited input voltage range.